Electrostatic separator



Nov. 5, 1963 G. WEICHART 3,109,806

ELECTROSTATIC SEPARATOR Filed May 15, 1961 7 Sheets-Sheet 1 I NVEN TOR.

WNW

WKM

5, 1963 G. WEICHART 3,109,305

ELECTROSTATIC SEPARATOR Filed May 15, 1961 FIG. 4

7 Sheets-Sheet 2 INVENTOR M d-CA- Nov. 5, 1963 G. WEICHART ELECTROSTATIC SEPARATOR Filed May 15, 1961 '7 Sheets-Sheet 5 INVENTOR. M BY Nov. 5, 1963 G. WEICHART ELECTROSTATIC SEPARATOR '7 Sheets-Sheet 4 Filed May 15, 1961 Nov. 5, 1963 G. WEICHART 3,109,306

ELECTROSTATIC SEPARATOR Filed May 15, 1961 '7 Sheets-Sheet 5 "Q s Q E OR.

' INV NT L? E BY M WM Nov. 5, 1963 G. WEICHART 3,109,806

ELECTROSTATIC SEPARATOR Filed May 15, 1961 '7 Sheets-Sheet 6 Nov. 5, 1963 Filed May 15, 1961 G. WEICHART ELECTROSTATIC SEPARATOR 7 Sheets-Sheet 7 INVENTOR.

United States Patent 3,109,806 ELECTROSTATIC SEPARATGR Giinter Weichart, Hannover, Germany, assignor t0 Kali- Forschungs-Anstalt G.rn.b.H., Hannover, Germany Filed May 15, 1961, Ser. No. 110,027 Claims priority, application Germany May 21, 1960 15 Claims. (Cl. 209-129) The present invention relates to electrostatic separators, and more particularly, the present invention is concerned with electrostatic separators of the types which are used for separating mixtures of pulverulent materials while such pulverulent materials fall under the influence of gravitational force through an electrostatic field.

It is an object of the present invention to provide an electrostatic separator of improved efiectiveness.

It is another object of the present invention to provide an electrostatic separator capable of achieving improved separation of a mixture of pulverulent materials while the same flow downwardly a given distance, in other words, to achieve an improved separation in a separator of given dimensions. 7

It is still another object of the present invention to provide an electrostatic separator for the separation of a mixture of pulverulent material into its constituents, which will permit eifective separation in a simple and economical manner.

Other objects and advantages of the present invention willbecome apparent from a further reading of the description and of the appended claims.

With the above and other objects in view, the present invention contemplates in an electrostatic separator, in combination, positive and negative electrode means spaced from each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field across the same, means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of the passage so that the material will flow downwardly through the channel to the lower end thereof while simultaneously being subjected to the electric field between the positive and negative electrode means, and means for retarding the downward flow of the material through the passage located within the same in transversal direction thereto and spaced from the upper and lower ends thereof, whereby due to retardation of the downward flow of the material electrostatic separation of the same will be improved.

According to a preferred embodiment of the present invention, the means for retarding the downward flow of the pulverulent material comprise a plurality of substantially horizontally extending deflecting arrangements vertically spaced from each other and arranged in the passage spaced from the upper and lower ends thereof for retarding the downward flow of the material through the passage, each of the deflecting arrangements comprising a plurality of laterally spaced pairs of elongated baflle members each of the pair of bafiie members defining between themselves a downwardly converging slot, and the pairs of baflle members of adjacent vertically spaced deflecting arrangements being arranged in staggered relationship to each other, the distance between the adjacent pairs of bafile members within one deflecting arrangement being wider than the elongated openings at the lower ends of the downwardly converging slots and the distance between adjacent pairs of baflle members being chosen in such a manner relative to the width of the lower ends of the paths that portions of the pulverulent material which are not deflected by the electric field may flow downwardly in vertical direction through the plurality of vertically spaced deflecting arrangements, while electrostatic separation of the material will be improved due to retardation of the downward flow of portions thereof which are deflected by the baffle members.

Thus, the separator of the present invention provides in the area which is under the influence of the electrostatic field, a plurality of horizontally extending deflecting or retarding or bafiie members, which will effectively brake the free downward flow under the influence of gravitational force of the pulverulent mixture and thereby will achieve that the pulverulent material will remain subjected to the electrostatic field for a prolonged period of time.

The plurality of vertically spaced deflecting arrangements may be concentrated in the upper portion of the electrostatic separator, or may extend throughout substantially the entire height of the same.

According to the present invention, due to the retarding means or baffle members which are superposed upon each other and extend in transversal direction to the electrostatic field, the period of time during which the pulverulent material is exposed to the electrostatic field will be extended to a multiple of the time during which such material would be exposed to the electrostatic field if it were allowed to flow downwardly through such field under the influence of gravitational force without being impeded by the retarding means.

Broadly, however without limiting the invention to any such theory, it may be said that the period of time during which the material will be exposed to the electrostatic field in a separator according to the present invention as compared to passing through the separator unimpeded under the influence of gravitational force, is proportionate to the square root of the number of vertically spaced transversely extending retarding means. In other words, if four such transversely extending retarding means are provided, i.e. if the retarding means are arranged in four vertically spaced planes, the average time required for the flow of particles of the material through the electrostatic separator will be twice as long as the time that would be required if the material could flow downwardly through the separator unimpeded and solely under the influence of gravitational force. Due to the prolonged time during which the pulverulent material which is to be subjected to electrostatic separation remains under the influence of the electrostatic field, i.e. due to the retardation of the downward flow, the deflecting effect in the direction of the lines of electrostatic force will be multiplied.

This will result in a very considerable improvement of the separation result achieved according to the present invention by passing equal quantities of material through separators of equal size, or, if the separation yield of conventional separators is satisfactory, then, in a separator according to the present invention and of the same size as a separator without the inventive baflie inserts, a greater quantity of material can be processed in a given period of time, or, if a given quantity of material is to be separated so as to give a certain yield, then the separator required according to the present invention, will be of con U siderably smaller dimensions than a separator according to the prior art, i.e. without the retarding means according to the present invention, which'will give the same result It is also possible according to the present invention to arrange the deflecting inserts in the separator in such a manner that frictional contact between individual particles of the material which'is to be separated will be increased and this again will cause an increased electrostatic charging of the particles, thus improving their separation.

The novel features which are considered as characteristic for the invention are set forth in particlular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, in which:

FIGS. 1-3 are schematic elevational views of three different embodiments of electrostatic separators according to the present invention;

FIG. 4 is a fragmentary schematic perspective view of a separator according to the present invention;

FIG. 5 is a plan view of another embodiment of a separator according to the present invention;

FIG. 6 is an elevational cross-sectional view taken along line 66 of FIG. 5;

FIG. 7 is a schematic fragmentary perspective view of another embodiment of a separator according to the present invention;

FIG. 8 is a plan view of yet another embodiment of the present invention;

FIG. 9 is a cross-sectional view taken along line 99 of FIG. 8;

FIG. 1O is a plan view of still another embodiment of the present invention;

FIG. 11 is a cross-sectional view taken along line '11-11 of FIG.

' FIG. 12 is a plan view of a further embodiment of the present invention;

FIG. 13 is an elevational cross-sectional view taken along line 13-13 of FIG. 12;

FIG. 14 is a plan view of still a further embodiment of the present invention;

FIG. 15 is a cross-sectional elevational View taken along line 15 15 of FIG. 14;

FIG. 16 is a plan view of yet another separator acembodiment of the present invention; and

FIG. 21 is a cross-sectional elevational View taken along line 2121 of FIG. 20.

Before referring to the drawings in detail, it should be noted that all of the drawings illustrate the invention in a schematic manner and, furthermore, that most of the drawings show the retarding means as comprising three vertically spaced arrangements extending transversely t0 the passage of the material through the electrostatic field, while some of the drawings illustrate only one substantially horizontal retarding means. It should be noted, that the number of vertically spaced arrangements is given for purposes of illustration only and that it is of course within the scope of the present invention to employ a different number of vertically spaced transversely extending retarding means. i

In all figures of the drawing, the electrodes are indicated by reference numeral '1, reference numeral 2 denotes the individual transversely extending retarding 4:. means, while a collecting device at the bottom of the electrostatic separator is identified by reference numeral 3.

In FIG. 3, reference numeral 5 indicates a resilient covering of the upper face of the flow retarding elements, scaffolding or support members for inserts 2 are indicated in some of the drawings by reference numeral 4 and in FIG. 20, a staggered or alternating arrangement of the openings in the inserts is indicated by reference numerals 6 or- 7, whereby reference numeral 6 denotes, for instance, the openings in the first, third and fifth honizontally extendingretarding element, while reference numeral 7 denotes the openings in the interposed horizontal retarding elements 2 and 4, so that matenial which flows downwardly through one opening 6 will be retarded and deflected by the next lower insert wherein the openings 7 are transposed or staggered relative to the next upper insert.

The individual inserts 2 are vertically spaced from each other, either equidistant, or so that the vertical distance between adjacent inserts increases in downward direction. This is illustrated in FIGS. 1 and 2 of the drawing. Particularly, the distance from the lowermost in- 'sert 2 to the collecting device 3 may be greater than the distance between adjacent inserts.

The individual insents, for instance, may be formed as a grid consisting of strips or rods which may be arranged parallel or perpendicular'to the direction of the electrostatic field, as illustrated in FIGS. 4 and 7. The upper face of the individual strips of the grid may be plane and extending horizontally, as shown in FIGS. 4-7, or may be trough-shaped as illustrated in FIGS. 8-11.

Thereby, the individual inserts are superposed upon each other in such a manner that the strips or rods of the individual superposed grids or inserts are staggered so that for instance a vertical line passing through an opening in'the uppermost grid will crossect a strip or rod or the like of the next lower grid. This is illustrated in FIGS. 8-11.

=By arranging the inserts or grids in'the above described manner, it will be accomplished that the major portion of the pulverulent material flowing or spilling downwardly through the separator will be deflected towards the center of the separator in a quantitative distribution which is somewhat similar to that of the statistical frequency curve according to Gauss which is illustrated and described, for instance, in Der Grosse Brockhaus, volume 4, pages 7 and 8, Wiesbaden 1954.

By arranging the individual strips or rods of the grids parallel to the direction of the electrostatic field, as illustrated in FIG. 4, this deflection towards the center will not influence electrostatic separation. However, if the individual strips or the like of the grid are arranged perpendicular to the direction of the electrostatic field, as illustrated in FIG. 7, then orientation and movement of the particulate material in the direction towards the electrodes will be hindered since accumulation of the pulverulent material will take place between the strips in the center of the electrostatic separator. Thus, it will depend on the specific type of pulverulent mixture and on the desired result, whether the individual strips or rods of the grid are to extend in the direction of the electrostatic field or in a direction perpendicular thereto.

Deflection of the downwardly flowing pulverulent material in the direction toward the center of the separator and parallel to the electrode plate can also be achieved by forming the individual grid element so as to have an upper face corresponding to the concave portion of a half cylinder wall having an axis which extends in horizontal direction and perpendicular to the direction of the electrostatic field. This alternative arrangement is illustrated in FIGS. 14 and 15.

As illustrated in FIGS. 16-19, it is also contemplated to arrange the individual grids so as to consist of pairs of strips which form a triangular, square or rounded trough formed with a slot in its lowermost portion, so that pulverulent material can flow downwardly through the elongated slot of the trough.

These troughs are so arranged in the plurality of superposed grids that a vertical plane passing through the slot of a trough of one grid will pass between two horizontally spaced troughs of the adjacent grid. As illustrated in FIGS. 16-19, the width x of the slot of the trough and the width y of the intervening space between two troughs of one grid differ from each other and the relationship between x and y is to be chosen in such a manner that material Which is not exposed to the influence of the electrostatic field would pass in a vertical stream downwardly through superposed spaces x and y, without being deflected.

The inserts may also be formed of perforated plates, screens or the like, which are arranged parallel to the lines of electrostatic force. Here too the arrangement of the superposed inserts or grids relative to each other is such that the openings in the vertically spaced grids are staggered relative to each other so that directly or vertically underneath the opening of one grid will be a portion of the plate of the adjacent lower grid and vice versa. This arrangement is illustrated in FIGS. 20 and 21.

Any insulating material possessing the required mechanical properties, such as glass, ceramic materials, synthetic materials and the like may be used for producing the grids of the present invention.

It is also within the scope of the present invention, as illustrated in FIG. 3, to cover the rigid grid material with a dampening layer of for instance rubber, synthetic or natural foamed materials or the like. Such dampening is desirable because it reduces scattering of pulverulent material hitting portions of the grid, which scattering has an unfavorable influence on the electrostatic separation. The same eifect, namely a reduction of scattering can be accomplished by forming the grid in accordance with FIGS. 8-11 so as to comprise elements of trough-shaped cross-sectional configuration. These troughs will be filled with pulverulent material and a portion of the kinetic energy of the downwardly falling particles will be absorbed by causing lateral movement of particles in the troughs. It has been found that a reduction in the scattering of particles will make possible an increase in the vertical distance between the individual inserts 2 so that the same separating effect can then be achieved with a reduced number of superposed inserts.

In the examples further below, several electrostatic separators according to the present invention are described and the results obtained with the same are compared with the results obtained by using conventional separators of the same overall dimensions, i.e. separators which lack the inserts of the present invention.

The examples are given as illustrative only without limiting the invention to the specific details thereof.

Broadly it may be said, without limiting the invention thereto, that the relationship between the starting material expressed in percent 'by weight of the constituent which is to be separated, the residue and the concentrate similarly expressed, may be represented by the following equation wherein A represents the yield, a the starting material, b the residue and c the concentrate (a, b, and being expressed in percent by weight as explained above):

The weight rate of flow is indicated in the examples in t/h.m, wherein t represents metric tons, h hours and m the width of the introduced stream of material in meters.

The separation-effecting potential is indicated in kv./cm., i.e. in kv. per cm. of distance between the two electrodes.

Example 7, in addition, gives the relationship between the widths of the slots at the lower ends of the more or less trough-shaped baflie members identified as x and the horizontal distance between adjacent troughs y. In this connection, reference is made to FIGS. 12, 13 and 16-20.

Under the conditions according to Example 7, the ratio X:y equals about 0.7:1.0. The vertical distance of the inserts according to Example 7 is about 6 cm. If the vertical distance between the grids is increased, then it is also desirable to increase the horizontal distance between adjacent troughs. In other words, if x is constant and the vertical distance between the grid arrangements is increased, y should become larger. On the other hand, if the vertical distance between adjacent grids is reduced, y will become smaller. The reason therefor is that the stream of pulverulent material passing downwardly from slots x has the tendency to become wider. The space y between adjacent troughs of the next lower grid arrangement serves the purpose of re-directing this stream. Thus, the width y must be adjusted to the width of the stream of downwardly flowing pulverulent material. Since the width of the stream of material increases with the distance between adjacent vertically spaced grid arrange ments, y will become greater with increasing vertical distance between adjacent grid arrangements.

EXAMPLE 1 Two electrostatic separators such as illustrated in FIGS. 5 and 6 are equipped with fifteen or eleven superposed grids spaced vertically from each other 27 or 36 mm. The entire grid arrangement occupies the upper 40 cm. of the separator, while the total vertical extension of the electrostatic field equals cm. The individual grids consist of glass strips having a width of 7 mm. and extend in the direction of the electrostatic field. As can be seen in FIG. 6, the individual glass strips of adjacent grids are arranged in staggered relationship so that any material flowing downwardly in vertical direction through the space between adjacent glass strips of an upper grid will contact a glass strip of the next lower grid.

The material which was subjected to electrostatic separation in the above described arrangement was sylvinite, type I having a particle size of between 0.1 and 0.75 mm.

The results obtained in the two above described separators according to the present invention and in a conventional separator are summarized in Table I.

Table I Electrostatic Separator 11 grids 15 grids No grids Starting material, percent K20 17. 5 17. 5 17. 5 Concentrate, percent K10 40. 7 43.1 31. 6 1. 7 l. 5 1.7 94. 2 94. 7 95. 4 Separating Potential k ./cm 3 3 3 Temperature, 0 50 .50 50 Vertical extension of separator, cm 120 120 120 Weight rate of flow, t/lLm O. 5 O. 5 0. 5 Electrode distance, cm 30 30 30 Width of introduction of material, cm... 10 10 10 The above table, in addition to showing the beneficial results of the grid arrangements according to the present invention, also indicates that increasing the number of grids without increasing the overall dimensions of the separator, will cause further improvement.

EXAMPLE 2 The purpose of this example is to illustrate the influence of the overall length of the separator, i.e. of the electrostatic field on the efliciency of the separation. In the upper portion of the separator twenty individual grids are arranged so as to form 10 double grids. The vertical distance between the two grids of one double grid is 9 mm., and the vertical distance between adjacent double grids equals 70 mm. The individual grids are formed of glass strips as described in Example 1, which are staggered in accordance with Example 1. The total height of one separator equipped with the above described multiple grid arrangement was 80 em, while the total height of the other subjected to electrostatic separation and the following resuits were obtained:

T able II Electrostatic Separator No grids Separator Separator Height Height, Height, 5 ,80 cm. 1.20 cm.

20 grids 20 grids S 120 cm. cm.

Starting material, percent K 0 17. 5 17. 5 17. 5 17. 5 Concentrate, percent K 35. 2 42.0 27.6 31. 6 Residue, percent K20 2.1 1. 9 2.1 1.7 20 Yield, percent. 93. 6 93. 4 95. 2 95. 4 Separating poten 3 3 3 3 Temperature, 50 50 50 50 Weight rate of flow, t/h.n1 0.5 0. 5 0. 5 0. 5 Electrode distance, em 30 30 30 30 Width of introduction of material, cm 0 10 10 10 The same comparison experiments were then carried out with hard salt having a particle size of between 0.1 and 0.75 mm. and the following results were obtained:

Table III Electrostatic Separator No grids Separator Separator Height Height, Height, 80 cm. 120 cm 20 grids 2O grids 80 120 cm cm.

10. 8 10. 8 10. 8 l0. 8 25. 1 27. 7 16. 7 17.0 1. 5 1. 5 1. 7 1. 6 Yield, percent 91. 6 91. 0 9a. 8 94. 0 Separating potential, lrv./em 3 3 3 3 Temperature, C 50 5O 50 4F Weight rate of flow, t/hm. 0. 5 0. 5 0. 5 0. 5 0 Electrode distance, cm 30 30 30 30 Width of introduction of material, nni 10 10 10 10 5O EXAMPLE 3 The separation of sylvinite H, particle size between 0.1 and 0.75 mm. was carried out in an electrostatic separator of the type illustrated in FIGS. 10 and 11 and also in an electrostatic separator of the type illustrated in FIGS. 5 and 6. In both cases, the individual grids are formed of elongated elements which extend in the direction of the electrostatic field. Three superposed grids are arranged within the upper 80 cm. of separators having a total length of 120 cm. The V-sh-aped grids are at a vertical distance of 320 mm. from each other. The V- shaped troughs of the grid elements according to FIGS. 10 and 11 will hold a portion of the pulverulent material and this cushion of pulverulent material will have a dampening eiiect on particles subsequently flowing downwardly through the separator. In contrast thereto, such dampening effect is missing in the separator according to FIGS. 5 and 6 wherein the particles hitting the grid elements with considerable speed will be reflected and scattered in all directions.

Table IV summarizes the results obtained in the two above-described cases and compares the same with the UTA ' results obtained under similar conditions with a conventional separator lacking the grid inserts of the present invention. 5

Table IV Electrostatic Separator (total height 120 cm.)

3 V-shaped 3 plane grids in grids in No upper upper 80 grids cm. cm.

Starting material, percent K20 17. 4 17. 4 17. 4 Concentrate, percent K30 48.1 39. 1 31. 6 Residue, percent K20- 1.5 2.1 1. 7 Yield, percent. 94. 3 92. 9 95. 4 S parating potenti 3 3 3 Temperature, C. 50 50 50 Weight rate of flow, 0.5 0.5 0.5 Electrode distance, cm. 30 30 30 Width of introduction of material, cm. 10 10 10 It can be seen that the dampening effect on the troughshaped grid elements will improve the results and it follows that the number of superposed grids required to achieve a desired result may he reduced by changing the upper surface configuration of the individual grid elements for instance from that shown in FIGS. 5 and 6 to that of FIGS. 10 and 11.

EXAMPLE 4 The separators used in this case included three superposed grids vertically spaced from each other at a distance of 15 cm. The uppermost grid was arranged directly beneath the upper end of the separator. The individual grid elements were such as are illustrated in FIGS. 5 and 6 and extended in the direction of the electrostatic field. The individual grid elements were formed of rigid synthetic material and had a width of 2 cm. However, in one case, the upper face of the individual grid elements was covered with a foam rubber layer having a thickness of 6 mm., substantially as illustrated in FIG. 3.

The material to be separated was fluorspar having a particle size of up to 1 mm. The results are shown in EXAMPLE 5 Separation in a separator according to FIGS. 14 and 15 is compared with separation in a conventional separator lacking grid inserts. The individual grid elements of the separator according to FIGS. 14 and 15 were formed of transversely curved strips of synthetic material which were so arranged that their upper faces defined part of a concave surface of a cylinder having an axis extending horizontally in a direction perpendicular to the direction of the electrostatic field. Two double grids were arranged in the separator, each double grid consisting of two individual grids vertically spaced 3 cm. from each other, while the vertical distance between the two double. grids was 30 cm'.

Siderite having a particle size of ,up to' 1 rnm.'was chosen as the material to be separated, and the results will be found in Table VI.

EXAMPLE 6 The separation of apatite having a particle size of up to 0.75 mm. was carried out on the one hand in an electrostatic separator according to FIGS. 20 and 21, and, on the other hand, in a conventional separator without grid inserts. Three plate-shaped inserts were arranged in the separator according to the present invention, vertically spaced 9 cm. from each other, with the uppermost plate 3 cm. below the upper end of the separator, i.e. the upper end of the electrostatic field. The results are shown in Table VII.

Table VII Electrostatic Separator With 3 grids ac- Without cording to grids Figs. 20 2l Starting material, percent apatite 44. 7 44. 7 Concentrate, percent apatite 75. 53. 7 Residue, percent apatite 24. 7 40. 1 Yield, percent t (36. 7 40. 6 Separating potential, kV./CH1 3 3 Temperature, C 70 Separator length, cm 120 120 Edge length of square openings in grid plates,

mm 20 W eight rate of flow, t.[h.m 0. 4 0. 4 Electrode distance, cm 30 30 Width of introduction of material, cm 10 EXAMPLE 7 A sulfur-containing mineral having particle sizes of up to 1.5 mm. was separated in the electrostatic separator illustrated in FIGS. 16 and 17, formed with troughs extending perpendicular to the direction of electrostatic force and having slots x at the bottom of the troughs extending throughout the entire length of the same. Three grids were arranged at a vertical distance from each other of 6 cm., whereby the uppermost grid was located 3 cm. below the upper end of the electrodes. The results obtained thereby are compared in Table VIII with the results obtained under similar conditions with a conventional separator lacking grid inserts.

Table VIII Electrostatic Separator With 3 grids Without according to grids Figs. 16 and 17 Starting material, percent S 15 Concentrate, percent S 75. 0 26 Residue, percent S. 2.0 4. 5 Yield, percent 89. O 84. 7 Separating potential, kv./crn 4 4 Temperature, C s 70 70 Separator length, cm 150 150 Ratio 1:1 (Figs. 16-17 about 0:7?1. 0 Weight rate of flow, t./h 5 Electrode distance, cm. 3O 30 Width of introduction of material, cm. 10 10 It will be understood that each of the elements de scribed above, or two or more together, may also find a useful application in other types of electrostatic separators dilfering from the types described above.

While the invention has been illustrated and described as embodied in an electrostatic separator, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In an electrostatic separator, in combination positive and negative electrode means spaced from each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field across the same; means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and grid means for retarding the downward flow of said material through said passage located within the same in transversal direction and spaced. from said upper and lower ends thereof said grid means being formed with a plurality of openings for downward passage of pulverulent material therethrough, whereby due to retardation of the downward flow of said material electrostatic separation of the same will be improved.

2. In an electrostatic separator, in combination, positive and negative electrode means spaced from each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field across the same; means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and grid means for deflecting the downward flow of said material through said passage located within the same in transversal direction thereto and spaced from said upper and lower ends thereof said grid means being formed with a plurality of openings spaced from each other and from said electrode means and adapted for the downward passage of pulverulent material therethrough, whereby due to deflection of the downward flow of said material electrostatic separation of the same will be improved.

3. In an electrostatic separator, in combination, positive and negative electrode means spaced from each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field across the same; means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and grid means for retarding downward flow of said material through said passage located Within the same in transversal direction thereto and spaced from said upper and lower ends thereof, said grid means including elongated rigid members having an upper face and a layer of resilient material cover- 1 1 ing at least said upper face, said grid means being formed with a plurality of openings spaced from each other and from said electrode means for downward passage of pulverulent material therethrough, whereby due to said retardation of the downward flow of said material electrostatic separation of the same will be improved.

4. In an electrostatic separator, in combination, positive and negative electrode means spaced from each other in lateral direction so as to define asubstantially vertical passage therebetween and forming an electrostatic field across the. same; means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative elec trode means; and grid means for retarding the downward flow of said material through said passage located within the same in transversal direction thereto and spaced from said upper and lower ends thereof, said grid means including rigid members having an upper face, and a layer of resilient foamed material covering at least said upper face'of said members, said grid means being formed with a plurality of openings for downward passage of pulverulent material therethrough, whereby due to retardation of the downward flow of said material electrostatic separation of the same will be improved.

5. Inan electrostatic separator, in combination, positive and negative electrode means spaced from each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field across the same; means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and grid means for retarding the down-,

ward flow of said material through said passage located within the same in transversal direction thereto and spaced from said upper and lower ends thereof, said grid means including a plurality of elongated, spaced members extending in said transversal direction, each of said members having a center portion at a lower elevation than the longitudinal edge portions thereof, said grid means being formed with a plurality of openings between said spaced members for downward passage of pulverulent material therethrough, whereby due to retardation of the downward flow of said material electrostatic separation of the same will be improved.

6. In an electrostatic separator, in combination, positive and negative electrode means spaced from'each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field across the same; means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly throughtsaid passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and grid means for retarding the downward flow of said material through said passage located within the same in transversal direction thereto and spaced from said upper and lower ends thereof, said grid means including a plurality of elongated, spaced members extending in said transversal direction, each of said members having an upper face of concave cross-section and said grid means being formed with a plurality of openings for downward passage of pulverulent material therethrough, whereby due to retardation of the downward flow of said material by said grid means electrostatic separation of the same will be improved.

7. In an electrostatic separator, in combination, positive and negative electrode means spaced from each 12 7 other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field across the same; means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and grid means for retarding the downward flow of said material through said passage located within the same in transversal direction thereto andtspaced'from said upper and lower ends thereof, said grid means including a plurality of elongated, spaced members extending in said transversal direction, each of said members having an upper face of substantially V-shaped crosssection, said grid means being formed with a plurality of openings for downward passage of pulverulent material therethrough, whereby due to retardation of the downward flow of said material electrostatic separation of the same will be improved. 7

8. In an electrostatic separator, in combination, positive and negative electrode means spaced from each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field: across the'same; means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and a plurality of grid means vertically spaced from each other for retarding the downward flow of said material through said passage located within the same in transversal direction thereto and spaced from said upper and lower ends thereof said grid means being formed with a plurality of openings spaced'from' each other and from said electrode means and adapted for the downward passage of pulverulent material therethrough, whereby due to retardation of the downward flow of said material electrostatic separation of the same will be improved.

9. In an electrostatic separator, in combination, positive and negative electrode means spaced from each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field across the same; means for introducing a pulverulent material adapted to be separated by electrostaticseparation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and a plurality of substantially horizontal grid means vertically spaced from each other for retarding the downward flow of said material through said passage located within the same in transversal direction thereto and spaced from said upper and lower ends thereof said grid means being formed with a plurality of openings spaced from each other and from said electrode means and adapted for the downward passage of pulverulent material therethrough, whereby due to retardation of the downward flow of said material electrostatic separation of the same will be improved.

10. In an electrostatic separator, in combination, positive and negative electrode means spaced from each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field across the same; means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and a plurality of grid means vertically spaced from each other, each of said grid means being formed with a plurality of openings therein spaced from said electrode means, and the openings of said vertically spaced plurality of grid means being arranged in staggered relationship for retarding the downward flow of said material through said passage said grid means being located within said passage in transversal direction thereto and spaced from said upper and lower ends thereof, whereby due to retardation of the downward flow of said material electrostatic separation of the same will be improved.

'11, In an electrostatic separator, in combination, positive and negative electrode means spaced from each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field across the same; means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and a plurality of substantially horizontally extending deflecting arrangements vertically spaced from each other and arranged in said passage spaced from the upper and lower ends thereof, for retarding the downward flow of said material through said passage, each of said deflecting arrangements comprising a plurality of laterally spaced pairs of elongated bafiie members each of said pair of bafile members defining between themselves a downwardly converging slot, and the pairs of baffle members of adjacent vertically spaced deflecting arrangements being arranged in staggered relationship to each other, the distance between said adjacent pairs of bafiie members within one deflecting arrangement being wider than the elongated openings at the lower ends of said downwardly converging slots and the distance between adjacent pairs of bafile members being chosen in such a manner relative to said width of the lower ends of said paths that portions of said pulver-ulent material which are not deflected by said electrostatic field may flow downwardly through said plurality of vertically spaced defleeting arrangements, while electrostatic separation of the material will be improved due to retardation of the downward flow of portions thereof which come in contact with said bafile members.

12. In an electrostatic separator, in combination, positive and negative electrode means spaced from each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field across the same; means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and a plurality of substantially horizontally extending deflecting arrangements vertically spaced from each other and arranged in said passage spaced from the upper and lower ends thereof, for retarding the downward flow of said material through said passage, each of said deflecting arrangements comprising a plurality of laterally spaced pairs of elongated baffie members each of said pair of bafiie members defining between themselves a downwardly converging slot, and the pairs of battle members of adjacent vertically spaced deflecting arrangements being arranged in staggered relationship to each other, whereby electrostatic separation of the material will be improved due to retardation of the downward flow of portions thereof which are deflected by said bafiie members.

13. In an electrostatic separator, in combination, positive and negative electrode means spaced from each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field across said passage; means for introducing a pulvemlent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and at least one substantially horizontally extended battle means arranged in said passage spaced from the upper and lower ends thereof for retarding the downward flow of said pulverulent material through said passage, said bafl'le means being toured with a plurality of openings therethrough distributed across said vertical passage and at least some of said openings being spaced from said electrodes.

14. In an electrostatic separator, in combination, positive and negative electrode means spaced from each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic field across said passage; means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and a plurality of substantially horizontally extended bafile means vertically spaced from each other and arranged in said passage spaced from the upper and lower ends thereof for retarding the downward flow of said pulverulent material through said passage, each of said bafile means being formed with a plurality of openings theret-hrough distributed across said vertical passage and at least some of said openings being spaced from said electrodes, the openings through adjacent ones of said vertically spaced bafile means being staggered so as to prevent uninterrupted vertical downward flow of pulverulent material through two successive balhe means, whereby, due to retardation of the downward flow of said pulverulent material, electrostatic separation of the same will be improved.

15. In an electrostatic separator, in combination, positive and negative electrode means spaced from each other in lateral direction so as to define a substantially vertical passage therebetween and forming an electrostatic held across said passage; means for introducing a pulverulent material adapted to be separated by electrostatic separation at the upper end of said passage so that said material will flow downwardly through said passage to the lower end thereof while simultaneously being subjected to said electrostatic field between said positive and negative electrode means; and a plurality of substantiallyhorizontally extended bafile means vertically spaced from each other and arranged in said passage spaced from the upper and lower ends thereof for retarding the downward flow of said pulverulent material through said passage, each of said bafile means comprising a plurality of elongated troughs located substantially within a horizontal plane and spaced from each other so as to form elongated openings between adjacent troughs extending transversal to said passage and being spaced from said electrodes, the troughs of adjacent ohm of said vertically spaced bafile means and the elongated openings between the same being arranged in staggered relationship so that pulverulent material flowing downwardly in vertical direction through an elongated opening of one of said baffle means will contact a trough of the next lower baille means, whereby the downward flow of said pulverulent material through said passage will be retarded and thereby electrostatic separation of the downwardly flowing pulverulent material will be improved.

References Cited in the file of this patent UNITED STATES PATENTS 2,899,055 Le Baron Aug. 11, 1959 FOREIGN PATENTS 847,431 Germany Aug. 25, 1952 

1. IN AN ELECTROSTATIC SEPARATOR, IN COMBINATION POSITIVE AND NEGATIVE ELECTRODE MEANS SPACED FROM EACH OTHER IN LATERAL DIRECTION SO AS TO DEFINE A SUBSTANTIALLY VERTICAL PASSAGE THEREBETWEEN AND FORMING AN ELECTROSTATIC FIELD ACROSS THE SAME; MEANS FOR INTRODUCING A PULVERULENT MATERIAL ADAPTED TO BE SEPARATED BY ELECTROSTATIC SEPARATION AT THE UPPER END OF SAID PASSAGE SO THAT SAID MATERIAL WILL FLOW DOWNWARDLY THROUGH SAID PASSAGE TO THE LOWER END THEREOF WHILE SIMULTANEOUSLY BEING SUBJECTED TO SAID ELECTROSTATIC FIELD BETWEEN SAID POSITIVE AND NEGATIVE ELECTRODE MEANS; AND GRID MEANS FOR RETARDING THE DOWNWARD FLOW OF SAID MATERIAL THROUGH SAID PASSAGE LOCATED WITHIN THE SAME IN TRANSVERSAL DIRECTION AND SPACED FROM SAID UPPER AND LOWER ENDS THEREOF SAID GRID MEANS BEING FORMED WITH A PLURALITY OF OPENINGS FOR DOWNWARD PASSAGE OF PULVERULENT MATERIAL THERETHROUGH, WHEREBY DUE TO RETARDATION OF THE DOWNWARD FLOW OF SAID MATERIAL ELECTROSTATIC SEPARATION OF THE SAME WILL BE IMPROVED. 